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PubMed2005

Continuous flash suppression reduces negative afterimages.

Illusions that produce perceptual suppression despite constant retinal input are used to manipulate visual consciousness. Here we report on a powerful variant of existing techniques, continuous flash suppression. Distinct images flashed successively at approximately 10 Hz into one eye reliably suppress an image presented to the other eye. The duration of perceptual suppression is at least ten times greater than that produced by binocular rivalry. Using this tool we show that the strength of the negative afterimage of an adaptor was reduced by half when it was perceptually suppressed by input from the other eye. The more completely the adaptor was suppressed, the more strongly the afterimage intensity was reduced. Paradoxically, trial-to-trial visibility of the adaptor did not correlate with the degree of reduction. Our results imply that formation of afterimages involves neuronal structures that access input from both eyes but that do not correspond directly to the neuronal correlates of perceptual awareness.

Figural Aftereffect↗
PubMedDate not supplied

Neural substrates of the tilt illusion.

PURPOSE: It has been suggested that direct and indirect tilt illusions and after-effects have different mechanisms, namely that the direct effects arise in VI and are sensitive to differences in spatial and temporal parameters between test and inducing stimuli, whereas indirect effects arise in extrastriate cortex and are insensitive to such parameters. When Wolfe (Vision Research 1984; 24: 1959-64) reported that large direct tilt after-effects occurred with short test flashes, he postulated that either there are distinct mechanisms which process brief and longer duration stimuli or that there are distinct mechanisms that are not primarily concerned with duration but are differentially responsive to temporal parameters amongst several others. RESULTS: In three experiments we demonstrate that large direct tilt illusions can be induced when parameters other than duration are manipulated, including contrast and spatial frequency, and that such large effects can occur when stimulus parameters are chosen to favour preferentially either the transient (magnocellular-like) system or the sustained (parvocellular-like) system. CONCLUSIONS: These results are thus consistent with Wolfe's second hypothesis. None of these stimulus manipulations had any effect on indirect tilt illusions, consistent with previous findings and hypotheses about the different mechanisms of the direct and indirect effects.

Brain↗
PubMed1978

Interocular transfer in individuals with strabismic amblyopia; a cautionary note.

Interocular transfer of the adaptation after effect was measured and correlated with residual binocular function for two strabismic amblyopes who represent different types of neural loss. The results indicate that for these two subjects there is paradoxical correlation between efficacy of interocular transfer and residual binocular function.

Adaptation, Ocular↗
PubMed1978

McCollough effect and eye optics.

Astigmatism induced by cylindrical lenses leads to colour sensations similar to the McCollough effect. Consequences for the design of experiments and a new interpretation of the McCollough effect are suggested.

Accommodation, Ocular↗
PubMed1980

Visual persistence as a function of spatial frequency and age.

Duration of visual persistance of sine-wave gratings of 1,2,4,8,12, and 16 cycles deg-1 was determined for seven-year-old, ten-year-old, and thirteen-year-old children. It was found that there was a decrease in persistence duration with age but the slope of this function for the different age groups did not change.

Adolescent↗
PubMed1980

Faces, vases, subjective contours, and the McCollough effect.

A version of the face-vase pattern was constructed with the use of subject contours. The McCollough effect was viewed on this pattern and it was found that perceptual alteration (face to vase) does not weaken the strength of the effect's hues while a complete perceptual rearrangement (faces/vases to concentric rectangles) does.

Accommodation, Ocular↗
PubMed1982

An effective paradigm for conditioning visual perception in human subjects.

Repeated pairing of an auditory conditioned stimulus with a weak visual unconditioned stimulus produced extended image sequences and visual responses conditioned to the tone alone. The experiment is set into the context of Pavlov's view of Helmholtz's "unconscious inference" thus providing experimental evidence linking the higher mental process of perception with classical conditioning.

Adolescent↗
PubMed1983

Afterimages, binocular rivalry, and the temporal properties of dominance and suppression.

When different contours are presented to the two eyes, an unstable percept, binocular rivalry, is the result. Parts of each set of contours may be seen but the two sets are not seen in the same place at the same time. The contours need not be physically present. Afterimages will produce binocular rivalry. Normal rivalry can be prevented if intermittent stimulation is used. Previous work has shown that orthogonal gratings, flashed for less than 150 ms and separated by more than 150 ms, will appear to fuse into a plaid or checkerboard pattern. In the present experiment this phenomenon is examined with afterimages used to produce rivalry. This abnormal 'fusion' is seen when negative afterimages are stroboscopically illuminated at less than 5 Hz. The results obtained with afterimages are predictable from the previous results obtained with stimuli external to the eye.

Adult↗
PubMed1983

Influence of spatial frequency, luminance, and duration on binocular rivalry and abnormal fusion of briefly presented dichoptic stimuli.

Orthogonal gratings, presented dichoptically, do not fuse into a single percept. Parts of each are seen while other parts are suppressed in an unstable perception (binocular rivalry). However, it has been previously noted that, if the gratings are briefly flashed, they will appear to fuse into a plaid or checkerboard pattern. Three experiments are reported which have been designed to define more clearly the spatial and temporal parameters of this effect in the hope that this would lead to better understanding of the normal mechanisms of dominance and suppression. Stimuli appear fused if flashed for less than 150 ms. The effect is independent of substantial changes in spatial frequency and luminance. Single flashes that appear fused when presented in isolation produce rivalry if separated by intervals less than about 150 ms. Intervals greater than 150 ms produce continued abnormal fusion. Possible mechanisms are discussed.

Adolescent↗
PubMed1983

Apparent movement induced by afterimages.

A small light source viewed in the dark through an afterimage produced by an electronic flash may appear to move along short random paths. Experiment 1 shows that this is not an instance of the autokinetic phenomenon, and experiment 2 shows that it is not related to the 'fluttering hearts' phenomenon. On the basis of experiments 1 and 3 it is concluded that small-scale ocular drifts, microsaccades, and possibly tremors cause the whole afterimage to move. The afterimage serves as a frame of reference and induces movement of the light source.

Adolescent↗
PubMed1990

The relationship between visual persistence and event perception in bistable motion display.

Observers viewed two alternating frames, each consisting of three rectangular bars displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three bars moving as a whole (group motion), and at short IFIs the overlapping elements in the two frames appeared stationary, while the third element appeared to move from one end of the display to the other (element motion). The upper temporal limit for perceiving element motion was reduced when bars with blurred edges were used and when either frame duration or bar size was increased. However, when inner and outer elements had different sizes, the element motion percept was dominant up to 230 ms IFI. These findings may be interpreted in terms of spatial tuning of motion mechanisms involved in the perception of bistable apparent motion.

Attention↗
PubMed1992

The perceived duration of gratings.

Since visible persistence of grating patterns increases with spatial frequency, it is often inferred that the perceived duration of a grating is also longer at higher spatial frequencies. However, other work has demonstrated that the perceived onset of a grating is also delayed at higher spatial frequencies. Thus it is impossible to infer the subjective duration from the results of visible persistence studies alone. In order to estimate perceived duration in the present study, reaction times (RTs) to grating onsets and offsets were measured for a range of spatial frequencies. The results indicate that although the perceived duration (ie the difference between offset and onset RTs) was consistently longer than the physical duration, the estimates of perceived duration did not vary with changes in spatial frequency. Differences between the present results and earlier findings are interpreted in the context of the different methods used to measure perceived offset.

Attention↗
PubMed1992

The apparent shape of afterimages in the Ames room.

When observers project afterimages of circular patterns onto a surface slanting away from them the images are reported as being oval in shape. In this paper it is reported that this does not occur when similar afterimages are projected onto the slanting rear wall of an Ames room. Instead of appearing as ovals, the afterimages remain circular. It appears as though the actually-slanted rear wall of the room not only looks as if it is normal to the line of vision, but also that it functions as if it was in such an orientation as far as a projection surface for afterimages is concerned. While these results are consistent with Emmert's law and with traditional accounts of shape and size constancy, they raise once again the age-old issue of whether the 'image on the retina' constitutes an object of perception that can be described in terms of its shape or size.

Adult↗
PubMed1992

An exploratory study of syncretic experience: eidetics, synaesthesia and absorption.

Synaesthesia and eidetic imagery are both syncretic experiences entailing a dedifferentiation of perceptual qualities. In this paper the correlation between synaesthesia and eidetic imagery is explored. Ten subjects selected for possible eidetic and/or synaesthetic ability were tested in a battery of tasks that tap structural and typographic eidetic imagery, and colour-hearing and colour-mood synaesthesia. It was found that both structural and typographic eidetic imagery were correlated with measures of synaesthesia, indicating a relationship between the two phenomena.

Adult↗